/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.expression;

import org.springframework.core.convert.TypeDescriptor;
import org.springframework.lang.Nullable;

/**
 * An expression capable of evaluating itself against context objects.
 * Encapsulates the details of a previously parsed expression string.
 * Provides a common abstraction for expression evaluation.
 *
 * @author Keith Donald
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public interface Expression {

    /**
     * Return the original string used to create this expression (unmodified).
     *
     * @return the original expression string
     */
    String getExpressionString();

    /**
     * Evaluate this expression in the default standard context.
     *
     * @return the evaluation result
     * @throws EvaluationException if there is a problem during evaluation
     */
    @Nullable
    Object getValue() throws EvaluationException;

    /**
     * Evaluate the expression in the default context. If the result
     * of the evaluation does not match (and cannot be converted to)
     * the expected result type then an exception will be returned.
     *
     * @param desiredResultType the class the caller would like the result to be
     * @return the evaluation result
     * @throws EvaluationException if there is a problem during evaluation
     */
    @Nullable
    <T> T getValue(@Nullable Class<T> desiredResultType) throws EvaluationException;

    /**
     * Evaluate this expression against the specified root object.
     *
     * @param rootObject the root object against which to evaluate the expression
     * @return the evaluation result
     * @throws EvaluationException if there is a problem during evaluation
     */
    @Nullable
    Object getValue(Object rootObject) throws EvaluationException;

    /**
     * Evaluate the expression in the default context against the specified root
     * object. If the result of the evaluation does not match (and cannot be
     * converted to) the expected result type then an exception will be returned.
     *
     * @param rootObject        the root object against which to evaluate the expression
     * @param desiredResultType the class the caller would like the result to be
     * @return the evaluation result
     * @throws EvaluationException if there is a problem during evaluation
     */
    @Nullable
    <T> T getValue(Object rootObject, @Nullable Class<T> desiredResultType) throws EvaluationException;

    /**
     * Evaluate this expression in the provided context and return the result
     * of evaluation.
     *
     * @param context the context in which to evaluate the expression
     * @return the evaluation result
     * @throws EvaluationException if there is a problem during evaluation
     */
    @Nullable
    Object getValue(EvaluationContext context) throws EvaluationException;

    /**
     * Evaluate this expression in the provided context and return the result
     * of evaluation, but use the supplied root context as an override for any
     * default root object specified in the context.
     *
     * @param context    the context in which to evaluate the expression
     * @param rootObject the root object against which to evaluate the expression
     * @return the evaluation result
     * @throws EvaluationException if there is a problem during evaluation
     */
    @Nullable
    Object getValue(EvaluationContext context, Object rootObject) throws EvaluationException;

    /**
     * Evaluate the expression in a specified context which can resolve references
     * to properties, methods, types, etc. The type of the evaluation result is
     * expected to be of a particular class and an exception will be thrown if it
     * is not and cannot be converted to that type.
     *
     * @param context           the context in which to evaluate the expression
     * @param desiredResultType the class the caller would like the result to be
     * @return the evaluation result
     * @throws EvaluationException if there is a problem during evaluation
     */
    @Nullable
    <T> T getValue(EvaluationContext context, @Nullable Class<T> desiredResultType) throws EvaluationException;

    /**
     * Evaluate the expression in a specified context which can resolve references
     * to properties, methods, types, etc. The type of the evaluation result is
     * expected to be of a particular class and an exception will be thrown if it
     * is not and cannot be converted to that type. The supplied root object
     * overrides any default specified on the supplied context.
     *
     * @param context           the context in which to evaluate the expression
     * @param rootObject        the root object against which to evaluate the expression
     * @param desiredResultType the class the caller would like the result to be
     * @return the evaluation result
     * @throws EvaluationException if there is a problem during evaluation
     */
    @Nullable
    <T> T getValue(EvaluationContext context, Object rootObject, @Nullable Class<T> desiredResultType)
            throws EvaluationException;

    /**
     * Return the most general type that can be passed to a {@link #setValue}
     * method using the default context.
     *
     * @return the most general type of value that can be set on this context
     * @throws EvaluationException if there is a problem determining the type
     */
    @Nullable
    Class<?> getValueType() throws EvaluationException;

    /**
     * Return the most general type that can be passed to the
     * {@link #setValue(Object, Object)} method using the default context.
     *
     * @param rootObject the root object against which to evaluate the expression
     * @return the most general type of value that can be set on this context
     * @throws EvaluationException if there is a problem determining the type
     */
    @Nullable
    Class<?> getValueType(Object rootObject) throws EvaluationException;

    /**
     * Return the most general type that can be passed to the
     * {@link #setValue(EvaluationContext, Object)} method for the given context.
     *
     * @param context the context in which to evaluate the expression
     * @return the most general type of value that can be set on this context
     * @throws EvaluationException if there is a problem determining the type
     */
    @Nullable
    Class<?> getValueType(EvaluationContext context) throws EvaluationException;

    /**
     * Return the most general type that can be passed to the
     * {@link #setValue(EvaluationContext, Object, Object)} method for the given
     * context. The supplied root object overrides any specified in the context.
     *
     * @param context    the context in which to evaluate the expression
     * @param rootObject the root object against which to evaluate the expression
     * @return the most general type of value that can be set on this context
     * @throws EvaluationException if there is a problem determining the type
     */
    @Nullable
    Class<?> getValueType(EvaluationContext context, Object rootObject) throws EvaluationException;

    /**
     * Return the most general type that can be passed to a {@link #setValue}
     * method using the default context.
     *
     * @return a type descriptor for values that can be set on this context
     * @throws EvaluationException if there is a problem determining the type
     */
    @Nullable
    TypeDescriptor getValueTypeDescriptor() throws EvaluationException;

    /**
     * Return the most general type that can be passed to the
     * {@link #setValue(Object, Object)} method using the default context.
     *
     * @param rootObject the root object against which to evaluate the expression
     * @return a type descriptor for values that can be set on this context
     * @throws EvaluationException if there is a problem determining the type
     */
    @Nullable
    TypeDescriptor getValueTypeDescriptor(Object rootObject) throws EvaluationException;

    /**
     * Return the most general type that can be passed to the
     * {@link #setValue(EvaluationContext, Object)} method for the given context.
     *
     * @param context the context in which to evaluate the expression
     * @return a type descriptor for values that can be set on this context
     * @throws EvaluationException if there is a problem determining the type
     */
    @Nullable
    TypeDescriptor getValueTypeDescriptor(EvaluationContext context) throws EvaluationException;

    /**
     * Return the most general type that can be passed to the
     * {@link #setValue(EvaluationContext, Object, Object)} method for the given
     * context. The supplied root object overrides any specified in the context.
     *
     * @param context    the context in which to evaluate the expression
     * @param rootObject the root object against which to evaluate the expression
     * @return a type descriptor for values that can be set on this context
     * @throws EvaluationException if there is a problem determining the type
     */
    @Nullable
    TypeDescriptor getValueTypeDescriptor(EvaluationContext context, Object rootObject) throws EvaluationException;

    /**
     * Determine if an expression can be written to, i.e. setValue() can be called.
     *
     * @param rootObject the root object against which to evaluate the expression
     * @return {@code true} if the expression is writable; {@code false} otherwise
     * @throws EvaluationException if there is a problem determining if it is writable
     */
    boolean isWritable(Object rootObject) throws EvaluationException;

    /**
     * Determine if an expression can be written to, i.e. setValue() can be called.
     *
     * @param context the context in which the expression should be checked
     * @return {@code true} if the expression is writable; {@code false} otherwise
     * @throws EvaluationException if there is a problem determining if it is writable
     */
    boolean isWritable(EvaluationContext context) throws EvaluationException;

    /**
     * Determine if an expression can be written to, i.e. setValue() can be called.
     * The supplied root object overrides any specified in the context.
     *
     * @param context    the context in which the expression should be checked
     * @param rootObject the root object against which to evaluate the expression
     * @return {@code true} if the expression is writable; {@code false} otherwise
     * @throws EvaluationException if there is a problem determining if it is writable
     */
    boolean isWritable(EvaluationContext context, Object rootObject) throws EvaluationException;

    /**
     * Set this expression in the provided context to the value provided.
     *
     * @param rootObject the root object against which to evaluate the expression
     * @param value      the new value
     * @throws EvaluationException if there is a problem during evaluation
     */
    void setValue(Object rootObject, @Nullable Object value) throws EvaluationException;

    /**
     * Set this expression in the provided context to the value provided.
     *
     * @param context the context in which to set the value of the expression
     * @param value   the new value
     * @throws EvaluationException if there is a problem during evaluation
     */
    void setValue(EvaluationContext context, @Nullable Object value) throws EvaluationException;

    /**
     * Set this expression in the provided context to the value provided.
     * The supplied root object overrides any specified in the context.
     *
     * @param context    the context in which to set the value of the expression
     * @param rootObject the root object against which to evaluate the expression
     * @param value      the new value
     * @throws EvaluationException if there is a problem during evaluation
     */
    void setValue(EvaluationContext context, Object rootObject, @Nullable Object value) throws EvaluationException;

}
